This invention relates to a system for controlling the rate of extension of a two stage telescoping mast of a materials handling vehicle.
In a materials handling vehicle, such as a turret stockpicker, an operator's platform mounted on a telescoping mast may be raised, along with a load handling assembly supporting load carrying forks, from floor level to the maximum height of the mast. The platform is raised until it reaches the top of the outer section of the mast. At this time, staging occurs, that is, as the platform is raised further, the platform picks up the outer section of the mast which telescopes on the inner or main section until the assembly reaches its maximum height, in the order of 35 feet.
When staging occurs, the weight of the structure being moved upwards is increased by the weight of the outer section of the mast, and in prior art vehicles, this sudden increase in weight causes a momentary deceleration that is severe enough to be uncomfortable to the operator. This is true even though shock absorbers are used between the platform and the outer mast section. Also, when the platform reaches its upper or lower limits, if this speed is not reduced, a sudden de-acceleration will result.